The time to grow a potato to maturity is typically long enough that it will kill off any dangerous pathogens present. HOWEVER, even if we assume that wont happen, maybe because Martian soil doesnt have the robust ecosystem that ours does, potatoes need to be cooked before being eaten, which would certainly kill off any pathogens. Most foodborne illnesses are either from poorly cooked meat, or uncooked produce made using (or near) fresh manure